1898.] MICROSCOPICAL JOURNAL. 197 



the rays from wliicli the photographic effect is to be ob- 

 tained. This produces a vast amount of useless inter- 

 ference of waves. I find that when I protect all those 

 parts from light, a much better result is obtainable with 

 a given amount of light. Hence in all cases where the 

 light is transmitted through the object the use of such a 

 light-shield from objective to condenser will still further 

 extend the probable limit of magnification. 



But there is a limit not so far away as that of the be- 

 fore mentioned photochemic sensitivity of light, namely, 

 the destruction of the energy of those rays within the 

 perfected camera by their mutual interference. This will 

 probably place the practical limit somewhere between 

 about ten million diameters and the much higher limit of 

 photochemic sensibility. 



By using monochromatic light this "interference" limit 

 will be at a much higher magnification than with white 

 light. If we could get light of only one wave length it 

 would certainly be quite useful to the new microscope, 

 but a narrow range of the best actinic portion of the 

 spectrum will do much better than polychromatic light. 



But monochromatic light is desirable for quite another 

 reason. It enables a much greater amount of light to be 

 concentrated upon the tissues being examined upon the 

 slide without acting as a burning glass to destroy the ob- 

 ject. Rays near the upper limit of the spectrum do not 

 so rapidly heat an object as the lower rays or as white 

 light. Hence I am arranging to focus the blue and 

 violet and ultra-violet rays upon a large prism, 

 parallelize them, and then transmit them through 

 the objective. By starting with a large area of monochro- 

 matic light I hope to get a much greater intensity of light 

 into the microscope than has hitherto been attempted. 

 As far as I know I s,hall have at least one hundred times 

 as much. This will extend the heretofore assigned limit 

 of photomicrography. 



